While not all games or writing sees the light of day, the experience is often worthwhile to help hone one's craft. Here are a list of projects I've worked on that had substantial effort (several months to several years) but never made it out the door.
Prototype title "Our Neighborhood" cooperative resource management game, Game Director - King Games
Beta title "Let's Dish" - cooperative Match 3, Game Design Director - Big Fish Skyrocket Studios
Prototype title "House Flip" cooperative Solitaire, Game Design Director - Big Fish Skyrocket Studios
Beta title "Gumball Heroes" flick battler, Game Design Director - Big Fish Skyrocket Studios
Prototype title "Bejeweled Crafter", Creative Director - EA PopCap
Production title "Bejeweled Adventures", Creative Director - EA PopCap
Announced title "The Agency" mmo shooter, Design Lead - Sony Online Entertainment
Concept title "Hogwarts Online", Design Lead - Sony Online Entertainment
Concept title "Marvel Superheroes Online", Design Lead - Sony Online Entertainment
Prototype title "Necrocyde", Head Writer/Game Designer - NovaLogic
Concept title "Might & Magic Online", Design Lead - 3DO
among probably about a dozen games that got between a couple weeks to a couple months in pitch or concept
"Rag Doll" (horror, polish pass only for Full Moon Entertainment FX dept)
"Headliners" (dark comedy about competing serial killers)
"The Dream Of The Undying" (Vampire romance)
"Elven Enchantment" (high fantasy)
"The West Coast Contenders" (Superheroic Spoof)
"Rabbit Tales" (Animated children's tale)
"Dr. Mordrid 2" (fantasy/sci-fi)
Buffy The Vampire Slayer "Skate Rats" - Spec Script
Mad About You "That Damn Cat" - Spec Script
Agents of Eternity Series Treatment, (original episodic horror)
Pilot: "Flight into Fright"
Episode 1: "Stage Fright"
Episode 2: "The Tale of the Tamanus"
"Familiar Instincts", Submitted to Brick Moon Fiction
"The Hapless Debut", Submission for “Lankhmar: New Adventures of Fafhrd and The Gray Mouser.” White Wolf 9/1/1995, accepted but project got cancelled immediately after (and producer is in jail for unrelated crimes)
Oh well, you win some, you ... well, you learn something that usually comes back in another form some time later in life.